Epstein–barr Virus-Associated Lymphoproliferative Diseases

Epstein–Barr virus-associated lymphoproliferative diseases (also termed EBV-associated lymphoproliferative diseases or EBV+ LPD) are a group of disorders in which one or more types of lymphoid cells (a type of white blood cell), i.e. B cells, T cells, NK cells, and histiocytic-dendritic cells, are infected with the Epstein–Barr virus (EBV). This causes the infected cells to divide excessively, and is associated with the development of various non-cancerous, pre-cancerous, and cancerous lymphoproliferative disorders (LPDs). These LPDs include the well-known disorder occurring during the initial infection with the EBV, infectious mononucleosis, and the large number of subsequent disorders that may occur thereafter. The virus is usually involved in the development and/or progression of these LPDs although in some cases it may be an "innocent" bystander, i.e. present in, but not contributing to, the disease.

EBV-associated LPDs are a subcategory of EBV-associated diseases. Non-LPD that have significant percentages of cases associated with EBV infection (see Epstein–Barr virus infection) include the immune disorders of multiple sclerosis and systemic lupus erythematosus; malignancies such as stomach cancers, soft tissue sarcomas, leiomyosarcoma, and undifferentiated nasopharyngeal cancer; the childhood disorders of Alice in Wonderland syndrome; and acute cerebellar ataxia.

About 95% of the world's population is infected with EBV. During the initial infection, the virus may cause infectious mononucleosis, only minor non-specific symptoms, or no symptoms. Regardless of this, the virus enters a latency phase in its host and the infected individual becomes a lifetime asymptomatic carrier of EBV. Weeks, months, years, or decades thereafter, a small percentage of these carriers, particularly those with an immunodeficiency, develop an EBV+ LPD. Worldwide, EBV infection is associated with 1% to 1.5% of all cancers. The vast majority of these EBV-associated cancers are LPD. The non-malignant, premalignant, and malignant forms of EBV+ LPD have a huge impact on world health.

The classification and nomenclature of the LPD reported here follow the revisions made by the World Health Organization in 2016. This classification divides EBV+ LPD into five categories: EBV-associated reactive lymphoid proliferations, EBV-associated B cell lymphoproliferative disorders, EBV-associated NK/T cell lymphoproliferative disorders, EBV-associated immunodeficiency-related lymphoproliferative disorders, and EBV-associated histiocytic-dendritic disorders.

Pathophysiology

Lymphoid cells involved in EBV+ LPD

In the "germinal center model" for the normal maturation of B cells, naive B cells enter the germinal centers of lymph nodes and other lymphoid tissues and in the process of becoming competent for producing functional antibodies, mature into lymphoblasts, centroblasts, centrocytes, memory B cells, and ultimately plasma cells. During this maturation, the B cells rearrange their immunoglobulin genes at multiple sites. The first lymphoid cell type invaded by EBV is the naïve B cell. Following this invasion, the virus express genes that control this cell's advance through these maturation stages; it can force the naïve B cell that it infects to: arrest maturation at any of these stages; become undetectable as an infected cell by the host's immune system; proliferate excessively; and develop into a B cell-based LPD. The virus may also exit the B cell it initially infects; invade T- or NK cells; and cause these cells to avoid detection by the immune system, proliferate, and progress to a T- or NK cell-based LPD. The T cells that may become infected by EBV are natural killer T cells (NK cells), Gamma delta T cells (γδ T cells), cytotoxic T cells (CTL), helper T cells (T_h cells), and follicular B helper T cells (T_FH cells). The means by which EBV establishes an dendritic-histiocytic cell (i.e. follicular dendritic cell) infection are unclear. Follicular dendritic cells are connective tissue rather than lymphoid cells. They do, however, have a surface membrane receptor, CD21 (also known as complement receptor type 2), which EBV uses to enter B cells. EBV may escape their infected B cell to invade follicular dendritic cells through this CD21 entry pathway. However, it is also thought possible that the EBV may direct its infected lymphoid cell to mature into an apparent follicular dendritic cell.

Epstein–Barr virus infection

The Epstein-Barr virus (also termed human herpesvirus 4) belongs to the Herpes family of Group I double-stranded DNA viruses. It is spread by transfer from the oral/nasal secretions of an infected individual to the oral cavity of an uninfected individual. Once in the oral cavity, the virus invades, reproduces in, establishes its lytic phase in, and lyses (i.e. bursts open) epithelial cells that line the oral mucosa of the newly infected individual. The freed virus then invades naïve B cells located in submucosal lymphoid tissue e.g. tonsils or adenoids. Here, it establishes either a lytic phase that allows it to infect other lymphoid cells or expresses genes that suppress the lytic cycle and impose one of four latency phases. Initially, the virus establishes latency III by expressing nuclear proteins encoded by its EBNA-1, -2, -3A, -3B, -3C, LP, LMP-1, -2A, and -2B and BART genes; cell surface membrane proteins encoded by its LMP-1, -2A, and 3A genes; and microRNAs encoded by its EBER-1 and EBER-2 genes. The products of these genes immortalize, promote the growth and survival, and regulate the maturation of the infected B cell. However, products of some latency III genes (particularly the viral cell surface proteins) make the infected cell susceptible to attack by the host's immune system. The virus avoids this by limiting expression of its latency genes to EBNA-1, LMP-1, -2A, -2B, some BARTs, and the two EBERs. This Latency II pattern of gene expression continues the infected cells' immortalization and proliferation, helps the cells escape the immune surveillance, and forces them to differentiate (i.e. mature) into memory B cells. EBV may establish and maintain a Latency I state in its infected memory B cells by expressing only EBNA1 and the two EBER genes. The products of the latter genes keep the virus in a mostly dormant state. Finally, EBV may establish and maintain a Latency 0 phase by expressing only EBER genes. In latency 0, EBV is in memory B cells as fully dormant, non-reproductive viruses but in this, as in all of the other latency phases, it can revert to its lytic phase. The following table gives more information on the actions of the EBV latency genes.

EBV-associated reactive lymphoid proliferations

EBV-associated reactive lymphoid proliferations are a set of disorders in which B cells or NK/T cells proliferate as an apparent reaction to EBV infection. They are usually self-limiting, non-malignant disorders but have a variable possibility of progressing to a malignant lymphoproliferative disease.

Epstein-Barr virus-positive reactive lymphoid hyperplasia

EBV-positive reactive lymphoid hyperplasia (or EBV-positive reactive lymphoid proliferation) is a benign form of lymphadenopathy, i.e. swollen, often painful lymph nodes. The disorder is based on histologic findings that occur in the lymphoid tissue of mainly older individuals who were infected with EBV many years earlier. Immunodeficient individuals of any age may also suffer the disorder. In immunologically normal individuals, histologic findings include the presence of small B cells located in the extrafollicular or, rarely, the follicular area of normal or minimally hyperplastic lymph nodes. These cells are commonly EBV+, express EBER viral genes, and carry the virus in its latency I or II phase. These cells may also occur in the bone marrow. Individuals who are immunodeficient because of disease, immunosuppressive drugs, or old age immunosenescence may exhibit a more pronounced hyperplasia of affected nodes, higher numbers of EBV+ cells, and a more disseminated disorder termed polymorphic lymphoproliferative disorder. These disorders almost always resolve spontaneously but in very rare cases progress over months or years to EBV+ Hodgkin lymphoma or EBV+ diffuse large B-cell lymphoma of the elderly.

Epstein–Barr virus-positive infectious mononucleosis

Infectious mononucleosis (IM) is caused by EBV in ~90% of cases; the remaining cases are caused by human cytomegalovirus, adenovirus, or toxoplasma. HIV, rubella, and Hepatitis viruses A, B, and C can produce an illness resembling IM. The acute EBV infection is usually asymptomatic or mild in children <5 years old whereas 25–75% of adolescents and adults develop overt IM after infection. The signs and symptoms of IM occur within weeks of EBV infection. Most cases involve a self-limiting flu-like illness or a mild to moderate illness of fever, sore throat, enlarged, painful lymph nodes in the head and neck, and/or an enlarged spleen. These manifestations usually abate within 6 weeks. More severe cases persist beyond 6 weeks and may be accompanied by uncommon but serious complications such as hepatitis, anemia, thrombocytopenia, hemophagocytosis, meningoencephalitis, myocarditis, pericarditis, pneumonitis, parotitis, pancreatitis and, in rare but extremely severe cases, life-threatening complications such as rupture or the spleen or disease-transitions to other LPD such as hemophagocytic lymphohisiocytosis (HLH), chronic active EBV (CAEBV), or lymphoma.

During the infection's acute phase, individuals generally have high levels of infective EBV in their oral/nasal secretions plus high blood levels of EBV, atypical lymphocytes, CD8 T cells, and memory B cells (up to 50% of the latter cells are EBV+). The tonsils and cervical lymph nodes in these cases are hyperplasic and contain mixtures of normal-appearing lymphocytes, activated lymphocytes, plasma cells, and Reed–Sternberg-like cells. Many of these normal-appearing and activated B cells and a small percentage of the tissue's T and NK cells are EBV+ with the virus being mostly in its lytic cycle rather than latent phases. The diagnosis of mild IM cases is often overlooked or made based on clinical and routine laboratory findings. These cases as well as asymptomatic and more severe cases of EBV infection are diagnosed definitively as EBV-associated by finding during the initial infection period the Epstein–Barr virus, IgM antibody to EBV viral-capsid antigen (VCA-IgM), IgG antibody to VCA (IgG-VCA), and IgG antibody to EBV viral- capsid antigen (EBNA1-IgG) in the blood and/or finding EBV in the oral/nasal secretions. There are no controlled studies on the treatment of uncomplicated EBV+ IM. Short-term courses of corticosteroid drugs are often prescribed for patients afflicted with airways obstruction, autoimmune reactions (e.g. autoimmune anemia or thrombocytopenia), or other complications of the disease. Treatment of these and the severest IM cases generally use regimens directed at the specific features of each type of complication.

Epstein–Barr virus-related hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a rare disorder characterized by a systemic inflammatory or, in extreme cases, overwhelming cytokine storm condition. It is due to the pathological proliferation and activation of benign histiocytes, macrophages, and lymphocytes along with the excessive release of proinflammatory cytokines by these cells. HLH has two distinct types. Primary HLH (also termed genetic or familial HLH) is caused by loss of function (i.e. inactivating) mutations in genes that cytotoxic T and/or NK cells use to kill targeted cells such as those infected with EBV. These include mutations in the UNC13D, STX11, RAB27A, STXBP2, and LYST genes that encode elements needed for these cells to discharge toxic proteins into targeted cells; mutations in the PFP gene that encodes one of these toxic protein, perforin 1; and mutations in the SH2D1A, BIRC4, ITK1, CD27, and MAGT1 genes that encode proteins required for the development, survival, and/or other cell-killing functions of ctyotoxic T and/or NK cells.

Secondary HLH is associated with and thought to be promoted by malignant and non-malignant diseases that, like primary HLH, also weaken the immune system's ability to attack EBV-infected cells. Malignant disorders associated with secondary HLH include T-cell lymphoma, B-cell lymphoma, acute lymphocytic leukemia, acute myeloid leukemia, and the myelodysplastic syndrome. Non-malignant disorders associated with secondary HLH include: autoimmune disorders such as juvenile idiopathic arthritis, juvenile Kawasaki disease, systemic lupus erythematosus, the juvenile onset and adult onset forms of Still's disease, and rheumatoid arthritis; immunodeficiency disorders such as severe combined immunodeficiency, DiGeorge syndrome, Wiskott–Aldrich syndrome, ataxia telangiectasia, and dyskeratosis congenita); and infections caused by EBV, cytomegalovirus, HIV/AIDS, bacteria, protozoa, and fungi. Secondary HLH may also result from iatrogenic causes such as bone marrow or other organ transplantation; chemotherapy; or therapy with immunosuppressing agents; About 33% of all HLH cases, ~75% of Asian HLH cases, and nearly 100% of HLH cases caused by mutations in SH2D1A (see X-linked lymphoproliferatgive disease type 1) are associated with, and thought triggered or promoted by, EBV infection. These cases are termed Epstein-Barr virus-positive hemophagocytic lympphohistiocytosis (EBV+ HLH). In EBV+ HLH, the virus may be found in B cells but mainly infects NK and T cells, including cytotoxic T cells. The virus induces defects in the ability of cytotoxic T cells to kill other EBV-infected cells and causes them to overproduce pro-inflammatory cytokines. These cytokines stimulate histiocyte and macrophage development, activation, proliferation, and cytokine production. The excessive release of these cytokines (e.g. tumor necrosis factor-α, interferon-γ, Interleukin 1 beta, interleukin 18, and CXCL9) causes a systemic and often overwhelming inflammatory condition.

Primary HLH is most often seen in Asians <4 years of age while secondary HLH is most often seen in older children and adults of various races. Typically, the disorder presents with fever, decreased numbers of circulating white blood cells and/or platelets, enlarged liver and/or spleen, clinical evidence of hepatitis, and/or central nervous system disturbances such as irritability, decreased levels of consciousness, seizures, meningitis (i.e. neck stiffness, photophobia, and headache), impaired cranial nerve function, hemiplegia, ataxia (i.e. poor coordination of complex muscle movements), and reduced muscle tone. Laboratory studies show abnormal liver function tests, reduced levels of blood fibrinogen, impaired blood clotting, and high levels of blood ferritin, triglycerides, soluble interleukin-2 receptor, and, in EBV+ HLH cases, circulating EBV. In the latter cases, histological examination of lymphatic, bone marrow, liver, neuronal, and other involved tissues show infiltrations of small EBV+ T cells, scattered small bystander EBV+ B cells, reactive histiocytes, reactive macrophages, and, in ~70% of cases, hemophagocytosis, i.e. ingestion of erythrocytes, leukocytes, platelets, and/or their precursor cells by histiocytes and macrophages. (Evidence of hemophagocytosis is not critical for the diagnosis of HLH.) The EBV in infected lymphocytes is in its lytic cycle rather than any latent phase. Criteria consistent with the diagnosis of HLH, as developed by the Histiocytic Society (2004), include finding 5 of the 8 following signs or symptoms: fever ≥38.5 °C; splenomegaly; low blood levels of any 2 of the following, hemoglobin (<10 mg/L), platelets (<100,000/μL), or neutrophils <1,000/μl; either one or both of the following, blood fasting triglyceride levels >265 mg/dL or fibrinogen levels <150 mg/dL; hemophagocytosis in lymphoid tissue; low or absent NK cell activity as tested in vitro on blood cell isolates; elevated blood levels of ferritin; and elevated blood levels or the soluble IL-2 receptor. The finding of EBV in T cells of blood or involved tissues is required to diagnose the EBV-associatec disease.

Prior to 1994, the treatments used for HLH were generally unsuccessful with average response rates to therapeutic interventions of ~10% and median survival times of ~12 month. In 1994, the Histiocytic Society established a drug regimen of dexamethasone + etoposide that increased the response rate to 70%. This regimen is currently recommended, particularly for primary HLH in young children, as induction therapy for EBV+ HLH except in patients with the macrophage activation syndrome where pulse methylprednisolone is the preferred treatment. Response rates are somewhat higher in young children than adults and in primary rather than secondary disease. Following inductive therapy, allogenic hematopoietic stem cell transplantation preceded by a reduced intensity conditioning regimen has been employed selectively, particularly in cases with primary HLH, with early results reporting some success. The management of EBV+ HLH has been less successful than that for other causes of secondary HLH. Novel approaches to HLH particularly in cases of refractory or recurrent disease include the use of antithymocyte globulin, the DEP regimen (i.e. liposomal doxorubicin, etoposide, methylprednisolone), an anti-interferon gamma monoclonal antibody, and, particularly in patients with EBV+-HLH, rituximab.

Chronic active Epstein–Barr virus infection

Chronic active Epstein–Barr virus infection (CAEBV) (also termed chronic active EBV infection of T and NK cells, systemic form) is a rare LPD of children and, less often, adults. CAEBV presents as severe, persistent form of infectious mononucleosis (IM) or a severe LPD disorder that follows months to years after a symptomatic (i.e. IM) or asymptomatic EBV infection. Characteristic findings that are also diagnostic criteria for the disorder are: 1) symptoms similar to those in infectious mononucleosis but persist for >3 months; 2) high blood levels of EBV DNA (i.e. >25 viral copies per mg of total DNA); 3) histologic evidence of organ disease; 4) presence of EBV RNA (e.g. an EBER) in an afflicted organ or tissue; and 5) occurrence of these findings in individuals who do not have a known immunodeficiency, malignancy, or autoimmune disorder. Other symptoms of CAEBV include persistent or intermittent fever, enlargement of lymph nodes, spleen, and/or liver, severe mosquito bite allergy, rashes, herpes virus-like skin blistering, diarrhea, and uveitis. The disorder may take a protracted course without progression over several years or a fulminant course with life-threatening complications such as Hemophagocytosis (i.e. ingestion of blodd cells by histiocytes), myocarditis, liver failure, interstitial pneumonia, or rupture of the intestines. CAEBV can progress to a malignant type of EBV+ T-cell LPD such as aggressive NK cell leukemia, NK/T cell leukemia, or peripheral T cell lymphoma.

The disorder may involve EBV+ T, NK, or, rarely, B cells. In EBV+ T and NK cell-associated disease, the tissues affected by CAEBV usually exhibit an histology that is not suggestive of a malignancy: lymph nodes have areas of hyperplasia, focal necrosis, and small granulomas; spleen shows atrophy of white pulp with congested red pulp; liver contains infiltrations of small lymphocytes around portal vasculature and sinuses; and lung and heart have findings typical of interstitial pneumonitis and viral myocarditis, respectively. Erythrophagocytosis (i.e. ingestion of red blood cells by histiocytes) often occurs in the bone marrow, spleen, and/or liver. The principal EBV+ cells in these tissues are T cells in ~59%, both T- and NK cells in ~40%, and B cells in ~2% of cases. The involved lymphoid tissues in EBV+ B cell cases contain proliferating Immunoblasts (i.e. activated B cells), plasma cells, and Reed-Sternberg-lide cells. The EBV+ cells in CAEB express primarily LMP1, LMP2, and EBNA1 viral proteins and EBER microRNAs, suggesting that the virus is in its latency II phase. The mechanism underlying the development of CAEBV is unclear. However, patients with CAEBV have a hyper-inflammatory condition with elevated blood levels of the same cytokines (i.e. IL-1β, IL-10, and IFNγ) seen in hemophagocytic lymphohystiocytosis. Furthermore, the disease has a strong racial preferences for Eastern Asians. These associations suggest that there are strong genetic predispositions involved in the disease's development and that this development is driven by T- and/or NK cell production of inflammatory cytokines.

Initially, CAEBV may assume a relatively indolent course with exacerbations and recoveries. However, the disease almost invariably develops lethal complications such as single or multiple organ failures. Current recommendations based on studies in Japan suggest that patients diagnosed with CAEBV be treated early in their disease with an intensive 3 step sequential regimen: 1) immunotherapy (prednisolone, cyclosporine A, and etoposide; 2) cytoreduction (vincristine, cyclophosphamide, pirarubicin, and prednisolone or, alternatively, prednisolone and cyclosporine A); and 3) reconstruction: allogeneic hematopoietic stem cell transplant preceded by reduced intensity drug conditioning (i.e. etoposide and cytosine arabinoside followed by fludarabine, melphalan, anti-thymocyte globulin, methylprednisolone, and etoposide). Patients receiving this regimen obtained unusually high 3 year event-free and overall survival rates of >87%. Further studies are required to determine how long these event-free and overall survival rates endure.

Severe mosquito bite allergy

Severe mosquito bite allergy (SMBA) is a rare disorder which occurs mainly in young East Asians (median age 6.7 years). In most cases, it is a manifestation of CAEBV infection of the EBV+ NK cell type: ~33% of all individuals with CAEBV develop this allergy. SMBA has also been reported to occur in rare cases of EBV positive Hodgkin disease, hydroa vacciniforme, aggressive NK‐cell leukemia (also termed aggressive NK-cell leukemia/lymphoma), and extranodal NK/T-cell lymphoma, nasal type, as well as in EBV negative LPD such as chronic lymphocytic leukemia and mantle cell lymphoma. EBV+ SMBA is a hypersensitivity reaction. In CAEV, the best studied or the predispositions to the disorder, SMBA is characterized by the development of skin redness, swelling, ulcers, necrosis and/or scarring at the site of a mosquito bite. This is often accompanied by fever and malaise; enlarged lymph nodes, liver, and/or spleen; liver dysfunction; hematuria; and proteinuria. Afflicted individuals have increased blood levels of immunoglobulin E (which plays an essential role in the development of type I hypersensitivity reactions of the skin and other tissues) and EBV+ NK cells. In severer cases, the disorder is complicated by hemophagocytosis, NK/T-cell lymphoma, or aggressive NK cell leukemia. Diagnostically, the skin lesions show infiltrating NK cells in the epidermis and subcutaneous tissue with a small fraction of these cells being EBV+ with the virus in its latency II phase. A very high density of EBV+ NK cells in these lesions suggests the disorder has progressed to NK/T cell lymphoma or NK cell leukemia. While the disorder's etiology is unclear, it is thought that the mosquito salivary gland allergenic proteins trigger reactivation of EBV in latently infected NK cells. Upon reactivation, EBV genes such as LMP1 express products that induce immortalization, proliferation, and in some cases malignancy of the EBV reactivated NK cells. The best treatment for SMBA remains unclear. Mild and clearly uncomplicated cases can be treated conservatively focusing on obtaining relief of symptoms such as skin irritation, fever, and malaise. However, cases with evidence of significant complications of CAEFV such as the development of hemophagocytosis, NK/T cell lymphoma, or aggressive NK cell lymphoma, support the use of the chemotherapeutic regimens directed at these complications. Cases of EBV+ SMBA associated with clear evidence of concurrent aggressive CAEBV have been treated with relative success by the 3 step regimen used to treat CAEBV. Rare cases of SMBA have been reported to occur in individuals who have no apparent predisposing disease but later develop CAEBV. Such cases require careful evaluation and follow-up for development of a predisposing disorder.

Hydroa vacciniforme-like lymphoproliferative disease

Hydroa vacciniforme is a rare photodermatitis reaction in which sunlight causes itchy skin papules and vesicles that develop crusts and eventually become scarred tissue. The lesions occur primarily on the sun-exposed skin of the face and back of the hand. It is an EBV+ disorder in which most cases develop in children, follow a waxing and waning course, and resolve in early adulthood. However, the disorder can occur in adults. Furthermore, the disease in children or adults may progress to cause severe, extensive, and disfiguring skin lesions unrelated to sunlight exposure, facial edema, and systemic manifestations such as fever, weight loss, and enlargements of lymph nodes, liver, and/or spleen. These cases may progress to an EBV+ LPD such as T cell lymphoma, T cell leukemia, B cell lymphoma, or B cell leukemia. The milder and more aggressive forms of hydroa vacciniforme were initially termed classic hydroa vacciniforme and hydroa vacciniforme-like lymphoma, respectively, but extensive overlap between the two disease types lead the 2016 World Health Organization to reclassify them into a single disorder termed Hydroa vacciniforme-like lymphoproliferative disease and to be a subcategory of CAEBV. Histological examination of the skin lesions reveals infiltrating lymphocytes most of which are T cells and a minority of which are NK- or B- cells. In the skin lesions, EBV occurs primarily in the T cells and to a lesser extent NK cells. Marker studies indicate that the EBV in these cells is in latency phase II.

Treatment of the non-aggressive cases of hydroa vaccinforme-like lymphoproliferative disease follow standard dermatological practices for non-malignant diseases. For malignant cases of the disease, Immunotherapeutic drugs prednisone, interferon-α, chloroquine, and thalidomide) have given temporary remissions and improvements; standard chemotherapy and radiotherapy regimens used to treat lymphoma and leukemia have produced only transient benefits while often causing unacceptable toxicities. Cases of EBV+ hydroa vacciniforme-like lymphoproliferative disease associated with clear evidence of concurrent CAEBV have been treated with relative success by the 3 step regimen used to treat CAEBV.

Epstein–Barr virus-positive mucocutaneous ulcer

EBV+ mucocutaneous ulcer is a rare lymphoproliferative disorder in which infiltrating B cells cause solitary, well-circumscribed ulcers in mucous membranes and skin. The disorder afflicts individuals who have poor immune function because of old age, immunosuppressant diseases (e.g. HIV/AIDS), immunosuppressive drug therapy, or allogenic hematopoietic stem cell transplantation. Immunosuppressive drugs associated with the development of these ulcers include methotrexate (the most often cited drug causing the disease), cyclosporin A, azathioprine, mycophenolate, TNF inhibitors, tacrolimus, and topical steroids. It is thought that the reduce efficacy of immune surveillance associated with these predisposing conditions or treatments maintain EBV in a dormant state systemically but not where EBV+ B cells are prevalent, i.e. in afflicted mucous membranes and skin. Consequently, the EBV+ cells at these sites proliferate and destroy tissue to create ulcerating lesions.

Persons developing these ulcers are usually elderly. Their ulcers are typically isolated, occur in the oral mucosa and less commonly in skin or gastrointestinal tract mucosa. Besides pain at the ulcer site and local tissue destruction (which may be severe), individuals with EBV+ mucocutaneous ulcer are symptomless and lack lymphadenopathy (i.e. enlarged and painful lymph nodes), involvement in other tissues, or B symptoms. However, ulcers in the gastrointestinal tract may present with a variety of abdominal symptoms including acute emergency perforations. Unlike most other forms of EBV+LPD, EBV-associated mucocutantious ulcers are generally not associated with detectable blood levels of EBV. Microscopically, the ulcers consist of lymphocytes, including EBV+ B cells, sometimes a scattering of other EBV+ lymphoid cell types, and histiocytes, plasma cells, eosinophils, and scattered large immunoblasts which may closely resemble but are not the Reed–Sternberg cells seen in Hodgkin lymphoma. These Reed-Sternberg–like cells are EBV+ B cells that express the tumor marker cell surface membrane protein, CD30, the B cell surface membrane marker, CD20, and the proteins typical of the EBV replication cycle latency II or III phase.

In elderly individuals with no other cause for immunosuppression, EBV+ mucocutaneous disease may exhibit a relapsing and remitting course with their ulcers worsening but then regressing spontaneously. Persistent and/or severely symptomatic cases have had excellent responses to rituximab, a commercial monoclonal antibody directed against the CD20 protein present on B cells. Individuals developing these ulcers as a consequence of immunosuppressive therapy for other diseases generally have a remission after the dosages of the drugs used in their immunosuppressive treatment regimens are reduced. Most of these patients do not experience a relapse.

EBV+ B cell lymphoproliferative diseases

After its initial entry into B cells, the Epstein–Barr virus infects other B cells and in doing so may or may not cause a symptomatic disease viz., infectious mononucleosis. In either case, the virus soon switches to its dormant, viral latency 0 phase within memory B cells and the infected individual becomes an asymptomatic, lifelong EBV carrier. At any time thereafter, however, the virus may reactivate, enter either its lytic cycle, latency phase II, or latency phase III; spread to other lymphoid cells, and drive its infected cells to proliferate excessively, survive abnormally, and establish an EBV+ LPD.

Epstein–Barr virus-positive Burkitt lymphoma

Burkitt lymphoma occurs in three forms. Epidemic Burkitt lymphoma (eBL) is common in Africa, the Middle East, Brazil, Papua New Guinea, and other areas where malaria is endemic. It usually presents in children 4–7 years old and in almost all cases is associated with EBV infection. Sporadic Burkitt lymphoma (sBL) is rare. It occurs in children and, less commonly, older (>60 years) adults. It is found primarily in Northern and Eastern Europe, East Asia, and North America. There are ~1,200 cases/year in the USA. Only 10–15% of sBL cases are associated with EBV infection. The immunodeficiency-related form of Burkitt lymphoma (iBL) strikes 30–40% of individuals with HIV-induced AIDS and rare cases of patients who received a bone marrow or other organ transplant; in the latter cases, individuals have almost always received intensive chemotherapy and therefore are immunodeficient. About 30% of iBL cases are infected with EBV.

eBL commonly presents with a jaw mass; periorbital swelling due to an orbital tumor; or an abdominal mass caused by a tumor in the retroperitoneum, kidney, or ovary. Less commonly, it present as a sudden onset of paraplegia or urinary incontinence due to tumor infiltration into neural tissue. sBL commonly presents with abdominal pain, nausea, vomiting, and/or gastrointestinal bleeding caused by the growth of an abdominal tumor; a head or neck tumor in lymph nodes, tonsils, nose, sinuses, and/or oropharynx); or extensive bone marrow infiltrations by malignant tumor cells. iBL commonly presents with fever, other constitutional symptoms, and tumors in the gastrointestinal tract, bone marrow, liver, lung, and central nervous system. Histologic examination of BL-involved tissues shows infiltrations by a uniform population of rapidly proliferating (i.e. mitotic index approaching 100%) and rapidly turning over (i.e. cells not only rapidly proliferate but also rapidly die due to apoptosis) lymphocytes punctuated by intermittent clear spaces where macrophagess containing ingested dead cells give the tissues the impression of a "starry sky" pattern. The lymphocytes are primarily B cells (e.g., express CD20 and CD10 markers) with rare T cells evident only in the background. The B cells are derived mostly from germinal center B cells, contain EBV in latency I phase, and express high levels of EBNA1 and EBER viral products. Some cases also express other EBNA and the LMP2A products. EBNA1 and EBER proteins may contribute to the development and/or progression of BL by inhibiting the death by apoptosis of the cells they infect while the product of LMP2A may activate the infected cell's PI3K cell signaling pathway thereby stimulating this cell's proliferation.

The malignant B cells in all three forms of BL commonly have acquired chromosomal translocations involving their MYC gene. MYC is a proto-oncogene (i.e. a cancer-causing gene if appropriately mutated or overexpressed) located on the long ("q") arm of human chromosome 8 at position 24 (i.e. at 8q24). In ~90% of BL cases, MYC is translocated to the IGH (i.e. Immunoglobulin heavy chain) gene locus at position 14q32, the IGK (i.e. immunoglobulin kappa light chain) gene at position 2p12 ("p" stands for short chromosome arm), or the IGL (i.e. immunoglobulin lambda light chain) gene at position 22q11. These translocations bring MYC under the transcriptional control of these antibody-forming loci and thereby cause the MYC product, Myc to be overexpressed and continuously driving the infected cell to proliferate. Mutations in other genes of the infected cell may promote its malignancy, e.g. ~30% of BL cases harbor B cell P53 gene mutations which may promote cell survival. These alternate, potentially EBV-independent routes to malignancy and the fact that some BL cases do not involve EBV allow that many cases of EBV+ BL are not caused and/or promoted by EBV: the ubiquitous virus is the likely cause of almost all cases of eBL but be an innocent passenger virus in many cases of sBL and iBL.

Patients with any of the three forms of BL (with or without an association with EBV) are treated with multiple drug chemotherapy regimens. While past studies found much better results in children than adults using this approach, recent studies report that more aggressive chemotherapy regimens that include the intrathecal administration of drugs give better results. The COCOX-M-IVAC regimen (systemic cyclophosphamide, vincristine, doxorubicin, and high-dose methotrexate alternating with ifosfamide, etoposide, and cytarabine plus intrathecal methotrexate and cytarabine) give event-free 2 year response rates of >90% in both children and adults. Addition of rituximab, a monoclonal antibody against the CD20 antigen expressed on B cells, may be added to this or other multiple drug regimens. Autologous stem cell bone marrow transplantation has not improved the results of these regiments. Treatment of HIV-associated iBL is similar to, and has success rates comparable, to non-HIV BL, particularly when coupled with treatment directed at HIV although adults >40 years old have had poorer responses to these regiments. Cases refractory to these regimens have a poor prognosis with average overall 3 year survival rates of ~7%.

Epstein–Barr virus-positive lymphomatoid granulomatosis

EBV+ lymphomatoid granulomatosis (EBV+ LG, also termed lymphomatoid granulomatosis [LG]) is a rare disease that involves malignant B cells and reactive, non-malignant T cells; it is almost always EBV+. This LPD occurs primarily in middle aged males (male:female ratio 2:1). EBV+ LG usually (~90% of cases) presents as a lung disorder with coughing, hemoptysis, shortness of breath, and chest X-rays showing multiple nodular lesions at the base of both lungs. It may also evidence signs and symptoms caused by nodular or infiltrative lesions in the skin, central nervous system, kidney, liver, and/or peripheral nervous system, At presentation the disease usually does not involve lymph nodes. In rare cases it may not even involve the lung. The lesions in EBV+ LG consist of occasional large, atypical B cells located in a background of numerous reactive CD4+ Helper T cells, plasma cells, macrophages, and variable numbers of large atypical lymphoid cells which resemble immunoblasts, plasmablasts, or Reed–Sternberg cells. The lesions often center around and evidence destruction of small blood vessels but, paradoxically, do not contain well‑formed granulomas. Only the lymphoid B cells in the lesions are EBV+; these cells express LMP1 and EBNA2 viral proteins and therefore carry EBV in its latency III phase.

Individuals with the disease may be immune deficient due to subtle reductions in their immune function or, based on individual case reports, immunodeficiency diseases such as HIV/AIDS, common variable immunodeficiency, X-linked agammaglobulinemia, hypogammaglobulinemia, sarcoidosis, methotrexate-treated rheumatoid arthritis, or the Wiskott–Aldrich syndrome. They may also have, again based on case reports, a history of inflammatory/autoimmune diseases such as chronic hepatitis, ulcerative colitis, retroperitoneal fibrosis, or primary biliary cholangitis. EBV+ LG may progress to or become complicated by the non-malignant skin disease, lymphomatoid papulosis, or a second lymphoid malignancy such as Hodgkin lymphoma, mycosis fungoides, CD30+ anaplastic large cell lymphoma, follicular lymphoma, chronic lymphocytic leukemia, or diffuse large B cell lymphoma. EBV+ LG appears in part due to the virus causing its infected B cell to release chemokines which attract, and thereby stimulate T cells to injure tissues, particularly blood vessels. Impaired host immune function and failure of infected cells to express viral proteins recognized by cytotoxic T cells allows EBV+ B cells to evade the immune system and proliferate.

LG presents as one of three grades based on the histology of biopsied tissues: grade I (<5 EBV+ cells per high power microscopic field (hpf), no atypical cells/hpf, and minimal necrosis); grade II (5–20 EBV+ cells/hpf, occasional atypical cells/hpf, and moderate necrosis); and grade III (>20 EBV+ cells/hpf, predominance of atypical cells/hpf, and extensive necrosis). Grade I disease may not need therapy and, in rare cases, remits spontaneously. Grade II and severe grade I disease is treated with immune regimens that include various interferons and/or rituximab, a monoclonal antibody against the B cell protein, CD20. Grade III and severe grade II disease are treated with either high dose glucocorticoids; chemotherapy regimens such as CHOP, ICE, or Hyper-CVAD; or combinations of these treatments. However, the efficacy of interferon-α and rituximab in EBV+G is disputed.) While EBV+ LG often responds to these treatments, there are no controlled clinical trials proving their long-term therapeutic value. Medium survival times for all cases of the disease are ~4 years with many cases progressing to other lymphoid malignancies that shorten survival times.

Epstein–Barr virus-positive Hodgkin lymphoma

Hodgkin lymphoma (HL) falls into two histologic forms, nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) and classical Hodgkin lymphoma (cHL) with cHL being divided into nodular sclerosis (NSHD), mixed cellularity (MCHD), lymphocyte rich (LRHD), and lymphocyte depleted (LDHD) subtypes. EBV is found in 30% to 50% of HL cases, but occurs in ~90% of NSHD and MCHD but ≤10% of LRHD, LPHD, or NLPHD cases. HL involves the infiltration of T cells, B cells, macrophages, eosinophils, fibroblasts, and Reed–Sternberg cells (HRS cells, also termed Hodgkin Reed-Sternberg cells) into lymphoid and other tissues. HRS cells are large mono- or poly-nuclear cells which: 1) derive from lymph node and/or spleen germinal center B cells; 2) may contain EBV and viral products indicative of stage II latency; and 3) are the only malignant cells in, and the mediators of, HD. EBV in HRS cells are thought to play a role in the pathogenesis (i.e. development) of EBV+ HL. These cells express uniquely high levels of the virus's LMP1 gene. This gene product protein, LMP1, mimics activated human TNF receptors (e.g. CD40, CD40, and RANK) in continuously stimulating the NF-κB, PI3K and JAK-STAT signaling pathways which promote cell proliferation, survival, and production of cytokines that may suppress the EBV's lytic cycle to maintain the HRS cells viability. HRS cells also express the virus's LMP2A gene protein product which mimics the human BCR gene product) in promoting the survival of its parent cells. And, EBV, by undefined mechanisms, causes crippling mutations in the HRS cell's rearranged immunoglobulin G genes to prevent them from expressing immunoglobulins and inducing them to secrete cytokines which recruit the other cited cell types into the EBV+HL's pathological infiltrates. This helps create a local environment conducive for HRS cells to evade the immune system and proliferate.

EBV+ HL is more prevalent in young children and young adults but can occur in those over 80 years old, perhaps because of old age-related deterioration in immune system function, infectious diseases, or malnutrition. The incidence of EBV+ HD's in individuals with HIV/AIDS is also high, ~10-fold greater than the general population, but the causes for this is unclear. The presentation of EBV+ HL is similar to that of EBV-HL, e.g. fever, night sweats, weight loss in the setting of swollen lymph nodes, and/or evidence of tumor invasion of other tissues. Treatment of the EBV+ HD is also similar to EBV- HD and offers cure rates approaching 90%, although some population based studies have found a higher incidence of relatively adverse outcomes in older individuals with EBV+ HL.

Epstein–Barr virus-positive diffuse large B cell lymphoma, not otherwise specified

Diffuse large B-cell lymphoma (DLBCL) is the second most common type of lymphoma. It occurs primarily in elderly adults, far less frequency in younger adults, and rarely in children. Elderly adults present with B symptoms (i.e. fever, night sweats, and weight loss), swollen lymph nodes, and symptoms due to malignant cell infiltrations into the upper gastrointestinal tract, lungs, upper airways, and/or other organs. Younger individuals present with swollen lymph nodes but frequently do not have class B symptoms or involvement of extra-nodal tissues. It is a more aggressive disease in the elderly. Histologic features of DLBCL can be divided into three patterns based on the cell types in tissue infiltrates; the anplastic variant (~3% of cases) exhibits prominent Reed–Sternberg-like cells embedded in a background of histiocytes and lymphocytes; the immunoblastic variant (8–10% of cases) has 90% immunoblasts; and the centroblastic variant (80% of cases) is dominated by centroblasts. These histological features are typically accompanied by the invasion and destruction (i.e. necrosis) of small blood vessels. An alternative classification is based on the disease's cell of origin: germinal center B cell DLBCL (GCB-DLBCL) and activated B cell DLBCL (ABC-DLBCL). Uncommonly, DLBCL occurs by what is known as a Richter transformation of chronic lymphocytic leukemia (CLL) to an extremely aggressive form of DLBCL. Many of these transformations develop in EBV-associated CLL cases (~10–15% of all CLL cases are EBV-associated).

About 10–15% percent of DLBCL cases are EBV+. These cases, termed Epstein–Barr virus-positive (EBV+) diffuse large B cell lymphoma, not otherwise specified (EBV+ DLBCL), occur predominantly in East Asia and Mexico and less commonly in Europe and the USA. EBV+ DLBCL is distinguished from DLBCL (often termed diffuse large B-cell lymphoma, not otherwise specified, i.e. DLBCL, NOS) in that virtually all the large B cells in the tissue infiltrates of the EBV+ disease type express EBV genes characteristic of the virus's latency III (common in the elderly) or II (common in younger patients) phase. These large B cells in EBV+ DLBCL are centroblastic (i.e. activated) B-cells that express EBERs, LMP1, EBNA1, EBNA2, and other viral proteins; in >50% of cases, they also express classic B cell antigenic proteins such as CD20, BCL6, and CD15. The viral proteins may be responsible for activating their infected cells' NF-κB, STAT/JAK, NOD-like receptor, and Toll